In high powered pulsed lasers of the type useful in isotope separation as described particularly for uranium enrichment in U.S. Pat. No. 3,772,519, it is desired for utmost efficiency to have a repetition rate measured in the thousands of pulses per second. Such rates may be difficult to achieve with present day laser technology in a single, high powered, pulsed laser, and it may be desired to avoid the use of rotating elements for beam combining as shown in U.S. Pat. No. 3,924,937.